1. Field of the Invention
The present invention is generally related to a membrane and method for making the same, and more particularly to a porous silica aerogel composite membrane and method for making the same and a carbon dioxide sorption device.
2. Description of the Prior Art
Due to discharge large amount of greenhouse gas, global warming becomes serious day by day. Carbon dioxide among discharged gas has the largest discharge amount and thus various carbon dioxide capture techniques have been developed. These carbon dioxide capture techniques should be selected accordingly based on their application conditions and merits or demerits for various application environments.
The carbon dioxide capture techniques include, for example, cryogenic separation, physical adsorption, chemical adsorption, and membrane separation. Cryogenic separation uses pressurization and condensation to liquefy CO2 and then uses boiling point differences to separate CO2 by distillation. Due to high power consumption during cryogenic separation process, it is more suitable for high added value applications. Physical adsorption uses adsorption materials for gas separation, such as active carbon, molecular sieves, zeolites but the selection of the adsorption material affects the separation efficiency. The chemical absorption uses absorbents to absorb CO2. Besides, the carbon dioxide absorbent includes, for example, alkaline solution like sodium hydroxide solution, inorganic absorbent like sodium carbonate, potassium carbonate, and ammonia water, alkanolamine solution like primary alkanolamine, secondary alkanolamine, tertiary alkanolamine, and steric hindered alkanolamine solutions. Furthermore, for example, the aerogel sorbents disclosed in US patent publication no. 2013/0287661 is formed by amino-group containing alkoxysilane where the amino group is used to attract CO2.
Membrane separation uses a membrane as a barrier for allowing gas passage or blockage and utilizes different types of the separation mechanisms to achieve separation effect. For example, various membranes such as dense gas separation membrane, facilitated transport mechanism and porous mechanism can be used.
In the above carbon dioxide capture techniques, cryogenic separation and physical adsorption are suitable for high partial pressure of CO2 while chemical absorption and membrane separation are still applicable for low partial pressure of CO2. However, physical adsorption and chemical absorption have the problem of CO2 saturation of adsorption materials or absorbents. Membrane separation uses gas selectivity for separation and has a problem of little or limited CO2 processing quantity. Therefore, the method of combining chemical absorption and membrane separation is expected to not only increase the CO2 processing quantity but also circulate CO2 absorbents to resolve the saturation problem. Thus, a suitable membrane and a CO2 absorbent can be properly chosen to form a novel porous silica aerogel composite membrane and method for making the same and a carbon dioxide sorption device so as to achieve optimum CO2 sorption quantity and long-term effective CO2 capture for reducing operation cost of CO2 capture and reducing required energy consumption to fulfill the industrial requirements.